Rapidminer Reading an Example Set From a File Using Python

Python - Files I/O

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This chapter covers all the bones I/O functions available in Python. For more functions, delight refer to standard Python documentation.

Printing to the Screen

The simplest way to produce output is using the impress statement where you tin can pass zero or more expressions separated by commas. This function converts the expressions you pass into a cord and writes the result to standard output equally follows −

#!/usr/bin/python  print "Python is really a bully language,", "isn't it?"        

This produces the following upshot on your standard screen −

Python is really a great language, isn't it?        

Reading Keyboard Input

Python provides 2 built-in functions to read a line of text from standard input, which by default comes from the keyboard. These functions are −

• raw_input
• input

The raw_input Role

The raw_input([prompt]) role reads one line from standard input and returns it as a string (removing the trailing newline).

#!/usr/bin/python  str = raw_input("Enter your input: ") print "Received input is : ", str        

This prompts you to enter any cord and information technology would brandish aforementioned string on the screen. When I typed "Hello Python!", its output is like this −

Enter your input: How-do-you-do Python Received input is :  Hello Python        

The input Function

The input([prompt]) role is equivalent to raw_input, except that it assumes the input is a valid Python expression and returns the evaluated result to y'all.

#!/usr/bin/python  str = input("Enter your input: ") print "Received input is : ", str        

This would produce the following result against the entered input −

Enter your input: [ten*5 for ten in range(2,10,2)] Recieved input is :  [10, twenty, thirty, twoscore]        

Opening and Closing Files

Until now, you accept been reading and writing to the standard input and output. Now, we will encounter how to use actual data files.

Python provides basic functions and methods necessary to manipulate files by default. You can do most of the file manipulation using a file object.

The open up Function

Before you can read or write a file, you lot have to open up it using Python'south built-in open() function. This function creates a file object, which would be utilized to telephone call other support methods associated with it.

Syntax

file object = open(file_name [, access_mode][, buffering])        

Here are parameter details −

• file_name − The file_name argument is a string value that contains the name of the file that you desire to access.

• access_mode − The access_mode determines the mode in which the file has to be opened, i.e., read, write, suspend, etc. A complete list of possible values is given below in the tabular array. This is optional parameter and the default file access mode is read (r).

• buffering − If the buffering value is set up to 0, no buffering takes place. If the buffering value is i, line buffering is performed while accessing a file. If you specify the buffering value equally an integer greater than ane, then buffering action is performed with the indicated buffer size. If negative, the buffer size is the organization default(default behavior).

Hither is a list of the different modes of opening a file −

Sr.No.	Modes & Description
1	r Opens a file for reading only. The file pointer is placed at the beginning of the file. This is the default manner.
2	rb Opens a file for reading but in binary format. The file pointer is placed at the beginning of the file. This is the default mode.
3	r+ Opens a file for both reading and writing. The file pointer placed at the offset of the file.
four	rb+ Opens a file for both reading and writing in binary format. The file pointer placed at the offset of the file.
5	w Opens a file for writing only. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing.
6	wb Opens a file for writing only in binary format. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing.
seven	w+ Opens a file for both writing and reading. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing.
8	wb+ Opens a file for both writing and reading in binary format. Overwrites the existing file if the file exists. If the file does not be, creates a new file for reading and writing.
ix	a Opens a file for appending. The file arrow is at the end of the file if the file exists. That is, the file is in the append manner. If the file does not exist, it creates a new file for writing.
ten	ab Opens a file for appending in binary format. The file pointer is at the end of the file if the file exists. That is, the file is in the append mode. If the file does not be, information technology creates a new file for writing.
eleven	a+ Opens a file for both appending and reading. The file pointer is at the end of the file if the file exists. The file opens in the append mode. If the file does not be, it creates a new file for reading and writing.
12	ab+ Opens a file for both appending and reading in binary format. The file arrow is at the stop of the file if the file exists. The file opens in the append mode. If the file does not exist, information technology creates a new file for reading and writing.

The file Object Attributes

Once a file is opened and you lot have 1 file object, you can get various information related to that file.

Here is a list of all attributes related to file object −

Sr.No.	Attribute & Description
1	file.closed Returns true if file is closed, false otherwise.
2	file.manner Returns admission mode with which file was opened.
3	file.proper name Returns proper noun of the file.
four	file.softspace Returns false if infinite explicitly required with impress, true otherwise.

Example

#!/usr/bin/python  # Open a file fo = open("foo.txt", "wb") print "Proper name of the file: ", fo.proper name print "Closed or not : ", fo.airtight impress "Opening mode : ", fo.mode impress "Softspace flag : ", fo.softspace        

This produces the following result −

Name of the file:  foo.txt Closed or not :  Fake Opening mode :  wb Softspace flag :  0        

The close() Method

The close() method of a file object flushes any unwritten information and closes the file object, after which no more writing can be washed.

Python automatically closes a file when the reference object of a file is reassigned to another file. Information technology is a good practise to apply the close() method to close a file.

Syntax

fileObject.close()        

Example

#!/usr/bin/python  # Open a file fo = open("foo.txt", "wb") print "Proper noun of the file: ", fo.name  # Close opend file fo.close()        

This produces the following result −

Name of the file:  foo.txt        

Reading and Writing Files

The file object provides a set of access methods to make our lives easier. Nosotros would encounter how to utilise read() and write() methods to read and write files.

The write() Method

The write() method writes whatsoever string to an open file. It is important to note that Python strings can have binary data and not just text.

The write() method does not add a newline grapheme ('\n') to the terminate of the cord −

Syntax

fileObject.write(string)        

Here, passed parameter is the content to be written into the opened file.

Case

#!/usr/bin/python  # Open up a file fo = open up("foo.txt", "wb") fo.write( "Python is a cracking language.\nYeah its great!!\due north")  # Close opend file fo.close()        

The above method would create foo.txt file and would write given content in that file and finally it would shut that file. If you would open this file, information technology would have post-obit content.

Python is a smashing language. Yep its great!!        

The read() Method

The read() method reads a cord from an open file. It is important to annotation that Python strings can accept binary data. autonomously from text data.

Syntax

fileObject.read([count])        

Here, passed parameter is the number of bytes to exist read from the opened file. This method starts reading from the kickoff of the file and if count is missing, then information technology tries to read as much as possible, mayhap until the end of file.

Case

Allow's take a file foo.txt, which we created in a higher place.

#!/usr/bin/python  # Open up a file fo = open("foo.txt", "r+") str = fo.read(10); print "Read Cord is : ", str # Close opend file fo.close()        

This produces the following effect −

Read String is :  Python is        

File Positions

The tell() method tells you the electric current position within the file; in other words, the next read or write will occur at that many bytes from the beginning of the file.

The seek(offset[, from]) method changes the current file position. The offset argument indicates the number of bytes to be moved. The from statement specifies the reference position from where the bytes are to be moved.

If from is ready to 0, it means utilise the showtime of the file as the reference position and 1 means utilise the current position equally the reference position and if information technology is set to 2 then the terminate of the file would be taken as the reference position.

Case

Let us take a file foo.txt, which we created higher up.

#!/usr/bin/python  # Open up a file fo = open up("foo.txt", "r+") str = fo.read(ten) print "Read Cord is : ", str  # Cheque current position position = fo.tell() print "Current file position : ", position  # Reposition pointer at the get-go once again position = fo.seek(0, 0); str = fo.read(10) print "Again read Cord is : ", str # Close opend file fo.shut()        

This produces the post-obit outcome −

Read Cord is :  Python is Current file position :  10 Again read Cord is :  Python is        

Renaming and Deleting Files

Python os module provides methods that assist you lot perform file-processing operations, such as renaming and deleting files.

To use this module y'all demand to import it beginning and then y'all can telephone call any related functions.

The rename() Method

The rename() method takes ii arguments, the current filename and the new filename.

Syntax

os.rename(current_file_name, new_file_name)        

Example

Following is the case to rename an existing file test1.txt −

#!/usr/bin/python import bone  # Rename a file from test1.txt to test2.txt os.rename( "test1.txt", "test2.txt" )        

The remove() Method

You can use the remove() method to delete files by supplying the name of the file to exist deleted as the argument.

Syntax

os.remove(file_name)        

Instance

Post-obit is the case to delete an existing file test2.txt −

#!/usr/bin/python import bone  # Delete file test2.txt os.remove("text2.txt")        

Directories in Python

All files are independent within various directories, and Python has no problem handling these too. The os module has several methods that help you create, remove, and change directories.

The mkdir() Method

You can employ the mkdir() method of the os module to create directories in the electric current directory. You need to supply an statement to this method which contains the name of the directory to exist created.

Syntax

os.mkdir("newdir")        

Case

Post-obit is the example to create a directory test in the current directory −

#!/usr/bin/python import bone  # Create a directory "test" os.mkdir("test")        

The chdir() Method

Yous tin can apply the chdir() method to alter the current directory. The chdir() method takes an argument, which is the name of the directory that you want to brand the current directory.

Syntax

os.chdir("newdir")        

Example

Post-obit is the example to go into "/habitation/newdir" directory −

#!/usr/bin/python import bone  # Changing a directory to "/habitation/newdir" os.chdir("/home/newdir")        

The getcwd() Method

The getcwd() method displays the current working directory.

Syntax

os.getcwd()        

Example

Following is the example to give current directory −

#!/usr/bin/python import os  # This would give location of the electric current directory os.getcwd()        

The rmdir() Method

The rmdir() method deletes the directory, which is passed as an statement in the method.

Before removing a directory, all the contents in information technology should be removed.

Syntax

os.rmdir('dirname')        

Example

Post-obit is the example to remove "/tmp/test" directory. It is required to requite fully qualified proper name of the directory, otherwise information technology would search for that directory in the current directory.

#!/usr/bin/python import os  # This would  remove "/tmp/test"  directory. bone.rmdir( "/tmp/exam"  )        

File & Directory Related Methods

In that location are iii important sources, which provide a broad range of utility methods to handle and manipulate files & directories on Windows and Unix operating systems. They are as follows −

• File Object Methods: The file object provides functions to manipulate files.

• OS Object Methods: This provides methods to process files as well as directories.

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Source: https://www.tutorialspoint.com/python/python_files_io.htm